The charging of tolls for vehicles dependent on the number of their occupants is frequently used as a policy measure to regulate traffic density. A preferred application relates to high occupancy toll (HOT) lanes, which are road lanes actually reserved for vehicles with multiple occupants (high occupancy vehicles (HOV)), but may also be used by vehicles with fewer occupants so long as an appropriate occupant-dependent toll is paid for the usage.
To prevent the risk of violation associated with a self-declaration of the occupant number or the risk of error associated with a visual check by control personnel, electronic toll systems are being increasingly used that automatically detect the number of occupants and calculate a toll dependent thereon. These systems use electronic onboard units (OBUs) equipped with occupant detectors.
An overview of currently available systems is given in the publications “Automated Vehicle Occupancy Monitoring Systems for HOV/HOT Facilities—Final Report”, McCormick Ranking Corporation, Ontario, Canada, December 2004; Steven Schijns and Paul Matthews: “A Breakthrough in Automated Vehicle Occupancy Monitoring Systems for HOV/HOT Facilities”, 12th HOV Systems Conference Houston, Tex., 20 Apr. 2005; Ginger Goodin: “Verifying Vehicle Occupancy for HOT Lanes—A path Toward Automated Systems”, Violations Enforcement Summit, Boston, Mass., 20-31 Jul. 2007; and Ginger Goodin and John P. Wikander: “Out for the Count—Verifying Vehicle Occupancy: Prospects for an Automated Solution”, Tolltrans 2009, pages 44-49. The known systems propose, inter alia, weight, thermal, infrared, ultrasonic or radar sensors to detect the presence of occupants or biometric sensors to detect fingerprints, faces, heartbeat or lung functions of occupants. For the latter measurements, electrical sensors or pressure sensors have been used hitherto that measure flows within the body of the occupants or respiratory pressure fluctuations.
Radar sensors that can detect the weak periodic movements of the human body on the basis of vital functions such as heartbeat and breathing have recently been developed to detect the layout of occupant seating for intelligent airbag control (“smart airbags”). These radar sensors use either CW Doppler radar in the ultra-high frequency continuous-wave Doppler radar (UHF) range, or the new system of ultra-wideband (UWB) impulse radar (UWB-IR), which can measure the rhythmic movements of the chambers of the heart or lobes of the lungs in a non-contact manner through media such as clothing and body layers. For the theoretical basic principles of these sensors reference is made to the following publications that are expressly incorporated herein by reference: Jerry Silvious and David Tahmoush: “UHF Measurement of Breathing and Heartbeat at a Distance”, IEEE Radio and Wireless Symposium 2010, pages 567-570; Isar Mostafanezhad, Olga Boric-Lubecke and Victor Lubecke: “A Coherent Low IF Receiver Architecture for Doppler Radar Motion Detector Used in Life Signs Monitoring”, IEEE Radio and Wireless Symposium 2010, pages 571-574; and also Kyohei Otha, Katsushi Ono, Isamu Matsunami and Akihiro Kajiwara: “Wireless Motion Sensor Using Ultra-Wideband Impulse-Radio”, IEEE Radio and Wireless Symposium 2010, pages 13-16. Special applications of such Doppler radar and UWB impulse radar sensors for airbag control are described, for example, in patent publications US 2001/0042977 A1, DE 10 2005 020 847 A1 and U.S. Pat. No. 7,134,687 B2.